The complement system is a proteolytic cascade in blood plasma and a mediator of innate immunity, a nonspecific defense mechanism against pathogens. There are three pathways of complement activation: the classical pathway, the lectin pathway, and the alternative pathway. All of these pathways generate a crucial enzymatic activity that, in turn, generates the effector molecules of complement. The main consequences of complement activation are the opsonization of pathogens, the recruitment of inflammatory and immunocompetent cells, and the direct killing of pathogens. Blood coagulation is another series of proenzyme-to-serine protease conversions, culminating the formation of thrombin, the enzyme responsible for the conversion of soluble fibrinogen to the insoluble fibrin clot. Protease-activated receptors, such as those activated by thrombin, are members of G protein-coupled receptors and function as a mediator of innate immunity. The kallikrein-kinin system is an endogenous metabolic cascade, triggering of which results in the release of vasoactive kinins (bradykinin-related peptides). Kinin peptides are implicated in many physiological and pathological processes including the regulation of blood pressure and sodium homeostasis, inflammatory processes, and the cardioprotective effects of preconditioning.

Organismal Systems; Immune system
BRITE hierarchy

nt06136  Complement activation (viruses)
nt06164  Kaposi sarcoma-associated herpesvirus (KSHV)
nt06168  Herpes simplex virus 1 (HSV-1)
nt06171  Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Homo sapiens (human) [GN:hsa]

PMID:26489954

Bajic G, Degn SE, Thiel S, Andersen GR

Complement activation, regulation, and molecular basis for complement-related diseases.

EMBO J 34:2735-57 (2015)
DOI:10.15252/embj.201591881

PMID:25568220

Mathern DR, Heeger PS

Molecules Great and Small: The Complement System.

Clin J Am Soc Nephrol 10:1636-50 (2015)
DOI:10.2215/CJN.06230614

PMID:26082779

Merle NS, Church SE, Fremeaux-Bacchi V, Roumenina LT

Complement System Part I - Molecular Mechanisms of Activation and Regulation.

Front Immunol 6:262 (2015)
DOI:10.3389/fimmu.2015.00262

PMID:21811895

Oikonomopoulou K, Ricklin D, Ward PA, Lambris JD

Interactions between coagulation and complement--their role in inflammation.

Semin Immunopathol 34:151-65 (2012)
DOI:10.1007/s00281-011-0280-x

PMID:25705421

Kurosawa S, Stearns-Kurosawa DJ

Complement, thrombotic microangiopathy and disseminated intravascular coagulation.

J Intensive Care 2:65 (2014)
DOI:10.1186/s40560-014-0061-4

PMID:23110467

Hillmeister P, Persson PB

The Kallikrein-Kinin system.

Acta Physiol (Oxf) 206:215-9 (2012)
DOI:10.1111/apha.12007

PMID:17635716

Rau JC, Beaulieu LM, Huntington JA, Church FC

Serpins in thrombosis, hemostasis and fibrinolysis.

J Thromb Haemost 5 Suppl 1:102-15 (2007)
DOI:10.1111/j.1538-7836.2007.02516.x

PMID:26324800

Crooks MG, Hart SP

Coagulation and anticoagulation in idiopathic pulmonary fibrosis.

Eur Respir Rev 24:392-9 (2015)
DOI:10.1183/16000617.00008414

PMID:23911436

Christiaans SC, Wagener BM, Esmon CT, Pittet JF

Protein C and acute inflammation: a clinical and biological perspective.

Am J Physiol Lung Cell Mol Physiol 305:L455-66 (2013)
DOI:10.1152/ajplung.00093.2013

PMID:24924409

Alberelli MA, De Candia E

Functional role of protease activated receptors in vascular biology.

Vascul Pharmacol 62:72-81 (2014)
DOI:10.1016/j.vph.2014.06.001

PMID:20027185

Smith HW, Marshall CJ

Regulation of cell signalling by uPAR.

Nat Rev Mol Cell Biol 11:23-36 (2010)
DOI:10.1038/nrm2821

PMID:23564577

Ricklin D, Lambris JD

Complement in immune and inflammatory disorders: pathophysiological mechanisms.

J Immunol 190:3831-8 (2013)
DOI:10.4049/jimmunol.1203487

PMID:23564578

Ricklin D, Lambris JD

Complement in immune and inflammatory disorders: therapeutic interventions.

J Immunol 190:3839-47 (2013)
DOI:10.4049/jimmunol.1203200

PMID:25309880

Loof TG, Deicke C, Medina E

The role of coagulation/fibrinolysis during Streptococcus pyogenes infection.

Front Cell Infect Microbiol 4:128 (2014)
DOI:10.3389/fcimb.2014.00128

PMID:25979655

Jozsi M, Tortajada A, Uzonyi B, Goicoechea de Jorge E, Rodriguez de Cordoba S

Factor H-related proteins determine complement-activating surfaces.

Trends Immunol 36:374-84 (2015)
DOI:10.1016/j.it.2015.04.008